havent driven a ecoboost petrol, but driven a few tdci fiestas, decent enough torque.
my tdci mondeo is on 155,000 miles and has only had wear/tear items and routine servicing, recently went to alton towers at 'motorway speeds' no problem at all.
i am thinking of a new(er) car, i doubt it will be petrol for me.
EDIT:50mpg ave over the life of the car, worst ive had is 42mpg round town with aircon on full blast.
fiesta should be a fair bit better id imagine . . .

. Go for a test drive see which you preffer factor in your average journey length type of driving urban versus motorway.
We went for a 1.6 petrol over the diesel because it was more refined to drive and real world mpg is high 40s even with alot of short journeys.

Not sure about the ford ones but I've heard from both VAG and Fiat forums that it is extremely hard to get anything like the economy figures from the small petrols. You seem to have to drive them really gently. After all, if you have it on boost, there is as much air and fuel going in as there would be on a bigger engine. You need to keep the turbo out of it ie drive it like it is a 1l 3cyl car.